1. Technical Field
The present invention relates generally to a pneumatic radial tire. In particular, the present invention relates to improvements to the carcass and belt package of the tire.
2. Description of the Prior Art
The tire industry is continually seeking increases in service life of a tire. Significant improvements were made in service life with the introduction of the radial pneumatic tire. Lesser improvements have periodically been made in the service life of the tire since the introduction of the radial tire. An example of a prior art radial pneumatic tire is illustrated in FIG. 1. The tire typically includes a pair of axially spaced apart beads B. A carcass C extends between the beads and is secured at axially opposite end portions to a respective one of the beads. The carcass includes substantially parallel extending reinforcing members of a suitable material. Each of the reinforcing members is disposed in a substantially radial plane. A belt package BP is located radially outward of a crown portion of the carcass. A tread T is located radially outward of the belt package for engaging a ground surface.
The industry standard tire is typically controlled or specified by an Association in each country, which defines the size and load range for passenger car tires. In the U.S., the Tire and Rim Association has such a specification. A typical specification (FIG. 2) defines the outside diameter and the cross sectional width for each tire size, with a window to show the variations allowed in the industry. Prior art tires are typically in a range of values close to the center of this window. The average tire of this invention is at a relatively small value of the outside diameter and at a relatively large value at the cross sectional width.
An agency of the United States Government has promoted consumer awareness and interest in increased service life through Uniform Tire Quality Grading Standards which were recently introduced. Such standards require the tire manufacturers indicate a tread life index on the sidewall of each tire produced.
As a part of the total improvement in tire service life, the tire designer has a number of options. These options include changing the tread compound, tread designs, carcass profile, bead, belt package, and reinforcing member materials. However, such improvements in service life often lead to tradeoffs in other tire performance characteristics. It is generally believed by those skilled in the tire art that the ability to keep the "contact patch", or "footprint", of the tire in engagement with the ground surface without scrubbing of the tread elements is desirable. Scrubbing is defined as the relative motion or movement between the tread surface and the ground surface at the interface between the tire and the ground. Scrubbing can occur at any point in the contact patch, but is more likely to occur at the entrance and exit of contact or at the lateral edge of the contact. For example, when the radial tire was introduced, a decrease in scrubbing when compared to a then existing bias tire, was realized. This decrease in scrubbing was a result of a relatively flexible sidewall which allowed a vehicle on which the tire was mounted to move laterally while maintaining relatively good contact with the ground surface. Another feature leading to improved service life was the relative increased size of the contact patch generally resulting in improved contact stress distribution and decreased average stresses at the tire-to-surface interface. An attempt to decrease rolling resistance in a pneumatic radial tire is disclosed in U.S. Pat. No. 4,513,802. U.S. Pat. No. 4,513,802 discloses a radial tire having a modified sidewall configuration. The curvature of the sidewall was modified by moving the maximum width position to a radial position closer to the tread of the tire.
A heavy truck tire is disclosed in U.S. Pat. No. 4,915,151. U.S. Pat. No. 4,915,151 discloses three relationships for controlling, optimizing, or minimizing the growth of the carcass sidewall due to inflation. One relationship is for a point near the bead area. Another relationship is for the maximum tread width area. Yet another relationship is for the shoulder area.